Because of S3’s generic.class() naming scheme, both functions may initially look similar, while they are in fact unrelated.
t.test() is a generic function that performs a t-test. t.data.frame() is a method that gets called by the generic t() to transpose data frame input. Due to R’s S3 dispatch rules, t.test() would also get called when t() is applied to an object of class test
It returns an object of the class ecdf (empirical cumulative distribution function) with the superclasses stepfun and function. The ecdf object is built on the base type closure (a function). The expression, which was used to create it (rpois(100, 10)), is stored in the call attribute.
This code returns a table object, which is built upon the integer type. The attribute dimnames is used to name the elements of the integer vector.
We can see that t.test() is a generic because it calls UseMethod():
t.test## function (x, ...)
## UseMethod("t.test")
## <bytecode: 0x0000024b6630d678>
## <environment: namespace:stats># or simply call
sloop::ftype(t.test)## [1] "S3" "generic"Interestingly, R also provides helpers, which list functions that look like methods, but in fact are not:
tools::nonS3methods("stats")## [1] "anova.lmlist" "expand.model.frame" "fitted.values"
## [4] "influence.measures" "lag.plot" "t.test"
## [7] "plot.spec.phase" "plot.spec.coherency"When we create an object with class test, t() dispatches to the t.default() method. This happens, because UseMethod() simply searches for functions named paste0(“generic”, “.”, c(class(x), “default”)).
x <- structure(1:10, class = "test")
t(x)## [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
## [1,] 1 2 3 4 5 6 7 8 9 10
## attr(,"class")
## [1] "test"However, in older versions of R (pre R 4.0.0; when Advanced R was written) this behaviour was slightly different. Instead of dispatching to the t.default() method, the t.test() generic was erroneously treated as a method of t() which then dispatched to t.test.default() or (when defined) to t.test.test().
A: This is a simple application of sloop::s3_methods_class():
s3_methods_class("table")## # A tibble: 10 × 4
## generic class visible source
## <chr> <chr> <lgl> <chr>
## 1 [ table TRUE base
## 2 aperm table TRUE base
## 3 as.data.frame table TRUE base
## 4 Axis table FALSE registered S3method
## 5 lines table FALSE registered S3method
## 6 plot table FALSE registered S3method
## 7 points table FALSE registered S3method
## 8 print table TRUE base
## 9 summary table TRUE base
## 10 tail table FALSE registered S3methodInterestingly, the table class has a number of methods designed to help plotting with base graphics.